Preparation of dihaloxanthones



United States Patent ()ffice 3,178,450 PREPARATION OF DIHALOXANTHON ESEdward J. McNelis, Media, Pa., assiguor to Sun Oil Company,Philadelphia, Pa., a corporation of New Jersey No Drawing. Filed July24, 1961, Ser. No. 125,955 5 Claims. (Cl. 260-335) This inventionrelates to the preparation of dihaloxanthones and more particularly tohte preparation of 2,6- and 3,6-dihaloxanthones by the pyrolysis ofalkali metal 2,4-dihalobenzoates.

According to the invention an alkali metal salt of 2,4-dihalobenzoicacid in which the halogen is chlorine, bromine or fluorine is heated toa temperature in the range of 250-375 0., preferably 300-340 0., wherebythe salt is converted partly to 2,6- and 3,6-diha-loxanthones. There isalso formed in minor amount an ester which ism-halophenyl-2,4-dihalobenzoate. The alkali metal component of thestarting material can be any of the alkali metals, namely, lithium,sodium, potassium, rubidium and cesium.

The major reaction that takes place in the pyrolysis can be representedby the following equation:

0 ll OM wherein X represents the halogen.

The pyrolysis preferably is carried out at about atmospheric pressureand in a manner to exclude air and moisture from the reaction mixturewhile permitting escape of the released carbon dioxide. The temperatureshould be in the range of 25-0-375 C. and more preferably 300340 C. Thetime of heating the reaction mixture will vary depending mainly upon thetemperature used but generally will be in the range of 0.1-2.0 hours.

The product mixture from the reaction contains, in addition to the twodihaloxanthones and the ester above mentioned, alkali metal halide andsome unreacted starting material. The mixture can be worked up bydissolution in a suitable solvent such as benzene, acetone or ether,filtering to remove the alkali metal halide, washing with water toremove the unreacted starting material and then evaporating the solvent.A solution of the 3,178,450 Patented Apr. 13, 1965 residue in a suitablesolvent such as benzene can be passed through a chromatographic columncontaining alumina to separate the individual reaction products. Theorder in which the products pass out of the column is as follows: theester, the 2,6-dihaloxanthone and the 3,6- dihaloxanthone. By collectingthe eflluent in suitable fractions, these products can be isolatedindividually.

The following example is illustrative of the invention: 4.58 g. ofpotassium 2,4-dichlorobenzoate were placed in a glass tube which hadbeen urged with nitrogen and the tube was heated while the nitrogenpurge was continued. The mixture was heated to above 300 C. for 30minutes, the maximum temperature reached being 309 C. After cooling, thereaction mixture was triturated with benzene and filtered to separatepotassium chloride. The filtrate was washed with water to separateunreacted starting material. Upon acidification of the wash water, 0.916g. of 2,4-dichlorobenzoic acid was obtained. Solvent was evaporated fromthe washed material and then a concentrated solution of this material inbenzene was chromatographed in a column of acid washed alumina. Thefirst fraction oif the column contained 275 mg. of the above-mentionedester. After crystallization of this material from ethanol, it was foundto have a melting point of 98.5-99.5 C. and an analysis as follows:

g. of 2,6-dichloroxanthone. After crystallization of this product fromalcohol, it was found to have a melting point of 216-2l6.5 C. and acharacteristic ultraviolet absorption peak at 1055 Its analysis was asfollows:

Found Theoretical Percent C 58. 63 58. 89 Percent H 2. 38 2. 28 PercentCl 25.29 26.

The third fraction from the column contained about 0.326 g. of3,6-dichloroxanthone. After crystal-lizing this product from alcohol, itwas found to have a melting point of 183-l84 C. and characteristicultraviolet absorption peaks at 10.5,u, 11.58 and 11.85

The yield of dichloroxanthones based on the total material from thecolumn in the foregoing example was 53%. The selectivity for producingdichloroxanthones in the reaction was about 41%.

When other alkali metals are substituted for potassium and when thehalogen is bromine or fluorine in place of chlorine, substantiallysimilar results are obtained.

I claim:

1. Method of producing 2,6- and 3,6-dihaloxanthone which comprisesheating an alkali metal 2,4-dihalobenzoate in which the halogen isselected from the group con- 0 sisting of chlorine, bromine and fluorineto a temperature References Cited in the file of this patent in therange of 250375 C. UNITED STATES PATENTS 2. Method according to claim 1in which said temperature is in the range of BOO-340 C. 3078299 M cNelhs1963 3. Method according to claim 1 in which the halogen OTHERREFERENCES is chlorine i Noller: Chemistry of Organic Compounds, Chapter12, 4. Method according to claim 1 111 which the alkali 5th edition W.B. Saunders co Phi-1a delphia (1955).

metal is potassium.

Karrer: Organic Chemlstry, 2nd editlon, Elsevier Pub- 5. Methodaccording to claim 1 wherein potassium fishing CO, Inc, New York (1946).

2,4-dichlorobenzoate is heated.

1. METHOD OF PRODUCING 2,6- AND 3,6-DIHALOXANTHONE WHICH COMPRISESHEATING AN ALKALI METAL 2,4-DIHALOBENZOATE IN WHICH THE HALOGEN ISSELECTED FROM THE GROUP CONSISTING OF CHLORINE, BROMINE AND FLUORINE TOA TEMPERATURE IN THE RANGE OF 250-375*C.